Why are appliances, most equipment, sinks, & toilets stripped from homes before sale in New Zealand?
In the U.K., the inclusion or exclusion of major appliances during a house sale varies, and is generally by mutual agreement, or -- at least in the past -- if not specifically included in the contract on the basis of "£200 cash if you want them" kind of an arrangement. It would be expected that the integral ovens and cooktops which have become more popular in recent years over the traditional free-standing range would always be included unless otherwise stated though.
It would certainly be very odd to take the toilet or major sinks when moving though!

I believe that over in France it is -- or used to be -- pretty common for people to strip out virtually all "fancier" light fittings when moving and just leave the cables poking out of the ceiling for the next owner to install whatever lights he wanted.